Exercise is medicine. Known benefits of moderate-to-vigorous physical activity (MVPA) include improvements to cardiorespiratory fitness, obesity, bone health, cardiovascular disease risk factors, some cancers, and depression and anxiety symptoms. Nevertheless, <8% of US adults as measured by accelerometry meet MVPA guidelines. The majority of existing interventions to increase MVPA have been relatively static (with educational materials or components such as goals to engage in MVPA not changing over time) and at the individual level. Technological and theoretical advances make adaptive interventions (AIs) for MVPA feasible for individuals. Unlike static interventions, AIs have time-varying components that respond uniquely to an individual's performance and changing needs. AIs have potential to reduce treatment mismatch, increase adherence, enhance potency, and personalize behavioral medicine. Micro-incentives (MIs) that are smaller, sooner incentives for goal attainment are possible with technology and hypothesized to result in greater MVPA than larger, later incentives. Combined MIs and AIs have the potential to enhance adoption of MVPA. Additionally, multilevel ecological models posit that physical activity is sensitive to the design of built environments. One core hypothesis derived from ecological models is that low walkable neighborhoods constrain physical activity adoption and maintenance, even in the context of individual-level interventions to increase such behavior. High walkable neighborhoods are hypothesized to provide a supportive environment for PA adoption and maintenance, enhancing the effect of individual-level interventions. Few studies have tested a priori the premise that individual-level interventions result in greater adoption and maintenance of MVPA when conducted in neighborhood environments supportive (vs. unsupportive) of physical activity. Based on our pilot work, we will develop novel adaptive (AI) and micro-incentive (MI) interventions and test them against static (SI) and delayed-incentive interventions (DI) in a 4-arm, randomized factorial trial to increase MVPA among 480 inactive men and women (18-60 years). Using GIS-measured neighborhood walkability and socioeconomic status, we will recruit participants from four neighborhood types: high walkable/high SES, high walkable/low SES, low walkable/high SES, and low walkable/low SES. The factorial design and sampling approach will allow us to test, within a multilevel framework, synergistic or antagonistic interaction effects of interventions and neighborhood factors on MVPA adoption and maintenance. Primary aims of this proposal are to (1) test main and interaction effects for AIs and MIs on MVPA minutes/day by 12 months, (2) investigate whether AIs and MIs foster persistence of MVPA at 18 and 24 months, and (3) determine whether AIs and MIs (compared to SIs and DIs) conducted in high walkable (vs. low walkable) neighborhoods result in greater adoption by 12 months and maintenance of MVPA at 18 and 24 months. Results will inform future hypotheses of ecological models and studies for MVPA adoption and maintenance to improve public health.